Block time and block size

As discussed before, each blockchain has a block time and a block size . Each network can have very different values and ways of handling block time. In Bitcoin, for instance, the block time is 10 minutes, while with Ethereum the block time is 20 seconds. In Stellar, the block time is about 4 seconds. These block times are determined by the code that runs the network. For networks such as Bitcoin, Litecoin, and Ethereum, the block time is actually an average. Because these are PoW networks, the block is finished once a miner solves the mining puzzle, which allows them to certify the block. In these networks, the difficulty of the puzzle is automatically adjusted so that on average the desired block time is reached.

The block size is the maximum amount of information that can be stored in each block. For Bitcoin, this is 1 MB of data's worth of transactions. For Ethereum, the limit is actually measured in GAS, a special unit of measuring both processing power (since Ethereum has smart contracts) as well as storage. Unlike Bitcoin, the GAS/storage limit for each block is not fixed but is instead adjusted by the miners dynamically.

It's important to note that blocks contain only possible information until they are finalized by the network. For instance, 1,000 transactions might happen, but if only 500 make it on to the next block, then only those 500 are real. The remaining transactions will continue to wait to be included into a future block.